Researchers Develop Recyclable Solar Cells From Trees

Since they already absorb energy from the sun and transform it, trees seem like a natural fit for solar-cell technology, which does ostensibly the same thing. Now, researchers from the Georgia Institute of Technology have come up with a way to use a natural material in trees to develop solar cells that pave the way for recyclable, sustainable, and renewable solar-cell technology.

To be clear, the part of the cell developed by Georgia Tech College of Engineering Professor Bernard Kippelen and his team that absorbs sunlight and transforms it into electricity is a chemical -- specifically, one derived from petroleum chemistry.

However, they have created the substrate of the cell, or its thickest part, with cellulose nano-crystal (CNC), which is derived from trees. Typically, this part of solar cells -- a thousand times thicker than the reactive material that does the energy conversion -- is fabricated on glass or plastic, neither of which is easily recyclable or eco-friendly.

Researchers at the Georgia Institute of Technology have derived material from trees to create a new solar cell that they believe paves the way for recyclable, sustainable, and renewable solar-cell technology. (Source: Georgia Institute of Technology)

CNC, on the other hand, is a natural material, and thus both of these things, Kippelen told Design News. “By replacing the substrate with natural materials, the solar cells can easily be recycled and separated into their components by immersing them in water,” he said. “That ease of recycling can make this technology greener than conventional photovoltaic technologies.” The yield of producing cellulose nanocrystals from dry wood is about 20 percent, he told us.

Kippelen learned of the possibility to create cell substrates with cellulose nanocrystals in early 2011 at an event organized by the Institute of Paper Science and Technology:

Learning that transparent substrates could be fabricated from biomass like wood was very intriguing since our main research deals with flexible and printed organic electronic devices. We study devices like light-emitting diodes and solar cells. Both type of devices are generally deposited on top of a transparent substrate.

Before fully embarking on his current research, he studied ardently about nanocellulose research, and met with fellow researchers from Purdue University, R.J. Moon and Jeff Youngblood, with whom he eventually collaborated on the technology.

Researchers are now working to increase the power conversion efficiency of the cells, which is currently 2.7 percent -- uncommonly high for cells with substrates derived from renewable raw materials, they said.

Kippelen and his team aim to optimize the optical properties of the cell’s electrode to improve the power-conversion efficiency of the cells to more than 10 percent, a level similar to cells fabricated with glass or plastic based substrates. They also have filed a provision technology patent for the technology with the US Patent Office.

Since the technology is in its nascent stages, it remains to be seen if and when the cells will make it into the commercial market. “At this time, we have validated the concept, and suggested a new path forward for greener renewable energy, but much research remains to be done before they can be manufactured and mass produced,” Kippelen said.

William, like Elizabeth I suspect that the researchers may have already figured out under just what circumstances water will make the cells break down. It's quite possible that, like other recyclable materials, this will only occur under certain circumstances, like the anaerobic conditions of landfills, or at certain temperatures.

Thanks for reporting on this, Elizabeth. Looks like a complete win-win to me, and a form of biomimicry we don't often see: using plant biology, not animal biology, as a model. I'm not surprised this comes from Georgia Tech--besides leading robotics research, they've also been working on alternative energy and power sources for a long time.

Yes, I totally see your point, William K, and solar systems typically last 20 to 25 years. I am pretty sure the designers of this cell are thinking of reliability as well and the cells won't just dissolve under a few drops of water. But I would have to speak more to them about the cells to find out for sure how the recylcling process works.

Elizabeth, my point is that giveen the cost and effort to set up a reliable solar cell system it only makes sense to have it last a while. After all, much of the expense is in the installation and supporting system, not in the cell arrays themselves. And based on what I have seen in many other products it is clear that a long product lifetime is not one of the concerns of the makers. Sometimes customers do force a reliability requirement to be considered, but it does not often happen.

I can see your concern, William K. But I think the idea is to recycle and reuse rather than have a product with a long lifespan that once it's over, becomes yet another piece of garbage in a landfill or in the ocean (where a lot of trash ends up). I am sure this process will be addressed and refined--and better explained--as scientists progress further in their research.

I see a serious rliability problem with solar cells that break down when watter is applied. This is because the intended product lifespan is over 20 years. Quick decomposition is just not the way for a product to last 20 years. Doesn't anybody else see a problem with that?

I see a serious rliability problem with solar cells that break down when watter is applied. This is because the intended product lifespan is over 20 years. Quick decomposition is just not the way for a product to last 20 years. Doesn't anybody else see a problem with that?

This is a good development. With the number of cells that would be required to be a viable energy source, the idea that they would not be easily recycled is a problem. It also adds to their carbon footprint. If course, the real problem with solar energy is not the cells, but energy storage. Until that is solved, their use will be limited.

Yes, if they can keep the price down then it could definitely be a good alternative to glass or plastic for solar cells, reducing use of synthetic materials and the waste those materials cause. Anything that can do that is definitely a step forward ecologically. While it's good to use natural energy like solar, sometimes the technology itself isn't doing much for the environment. Then again, I hope that if wood from trees is used to make cells, it is also replenished in some way.

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